Recently, use of dendritic cell vaccines in cancer treatment is gathering attention. The dendritic cell vaccine is prepared from dendritic cells derived from a subject (e.g., a cancer patient) to which the vaccine is administered, wherein a cancer antigen is incorporated into the dendritic cells (pulsed with a cancer antigen), and the vaccine is administered to the subject in vivo. The administered dendritic cells present the cancer antigen to T-cells, and the T-cells (CTL) presented with the antigen specifically attack cancer cells. It is therefore possible to treat cancer without damaging in vivo normal cells.
Incidentally, the dendritic cells necessary for producing a dendritic cell vaccine cannot be directly isolated from the body. Accordingly, dendritic cells are prepared by isolating monocytes from blood sampled from a subject to which the vaccine is administered and differentiating the monocytes into dendritic cells.
As a conventionally known method of sampling monocytes for producing a dendritic cell vaccine, a method of isolating leukocytes in blood with a blood component collecting apparatus (hereinafter, this method is referred to as “apheresis”) is known. In the apheresis, however, the practical use of the apparatus is expensive and the operation of the apparatus requires advanced skills. In addition, the apheresis collects a mixture containing not only monocytes but also components other than monocytes (e.g., leukocytes, erythrocytes, and platelets). Accordingly, a step of isolating mononuclear cells for removing components other than monocytes, such as erythrocytes and platelets, is usually performed after the apheresis.
In clinical application of a dendritic cell vaccine, approximate 1×107 cells are desirably used for one administration. In order to prepare such a number of cells, apheresis is usually carried out about eight times using one subject at intervals. Furthermore, since the ratio of monocytes contained in blood is small, if apheresis is employed for obtaining a sufficient amount of monocytes for producing a dendritic cell vaccine, it is necessary to sufficiently collect the leukocyte components by circulating the blood in an apheresis apparatus. This puts a very large burden on a patient physically and temporally. Accordingly, if the condition of the patient suddenly worsens during apheresis, the apheresis is discontinued, and the dendritic cell vaccine therapy itself must be abandoned in some cases. It is alleged that the amount of monocyte components collected by apheresis usually allows production of a dendritic cell vaccine that can be administered for about five to eight times, but the actual amount of the resultant dendritic cell vaccine varies depending on the blood conditions and other factors of a patient.
In a conventional method of collecting peripheral blood from, for example, an arm, the burden on a patient is light, but the method has a disadvantage that when the collected monocytes are directly differentiated into dendritic cells by a conventional method, a sufficient number of cells cannot be obtained. Accordingly, in order to produce a dendritic cell vaccine composed of a sufficient number of cells from monocytes prepared from collected peripheral blood, proliferation of the monocytes in the process of producing the vaccine is a problem to be solved, and a technology for overcoming it has been demanded. In such a technology, the period of time for producing a dendritic cell vaccine is desirably about two weeks in view of the dosing interval of the dendritic cell vaccine.
Accordingly, in order to solve the problem, in vitro proliferation of monocytes isolated from blood is proposed. As such a method, Patent Literature 1 discloses the culture of monocytes while preventing a specific material in the monocyte from being expressed. This method, however, needs a step of producing a recombinant and takes a long time for the culture. [Patent Document 1] Japanese Unexamined Patent Application (Translation of PCT Application), Publication No. 2010-515442